Polarized electromagnetic relays are known in configurations with three-pole permanent magnet (WO 93/23866) and with two-pole permanent magnet (U.S. Pat. No. 4,912,438, U.S. Pat. No. 5,153,543, U.S. Pat. No. 6,670,871 B1). In any case, the electromagnet includes a coil comprising a core and pole pieces in a yoke-shaped configuration. In case of a three-pole permanent magnet, this permanent magnet is arranged between the two legs of the yoke above the coil and in parallel to the axis of the coil. This permanent magnet may be separated from a magnetized strip and inserted into the coil former between the two legs of the yoke. In case of a two-pole permanent magnet, the latter is magnetically connected transversely to the axis of the coil, with one pole approximately in the middle of the old core (U.S. Pat. No. 4,912,438, U.S. Pat. No. 5,153,543).
From U.S. Pat. No. 4,975,666 a polarized electromagnetic relay is known comprising a base housing which opens to the top, with an electromagnetic block including coil, core, and pole legs, and a permanent magnet between the pole legs, and an armature block including armature and switch elements on the pole legs mounted therein. The assembly does not permit to produce the permanent magnet located between the pole legs from an unmagnetized ferromagnetic precursor by magnetization, because this would damage the coil by excessive induced currents.
From DE 195 20 220 C1, another polarized electromagnetic relay is known, in which the coil together with two ferromagnetic yokes and a permanent magnet interposed therebetween are inserted into a base body from above and fixed with a potting compound. Magnetizing of an unmagnetized precursor in the installed state is not possible.
Also, a relay is already known (U.S. Pat. No. 6,670,871 B1) including a two-pole permanent magnet which extends in parallel to the coil axis. The plate-shaped permanent magnet having poles on the top and bottom thereof is received in an armature plate. The electromagnet is accommodated in a two-part housing which comprises a trough-shaped lower portion and a box-shaped upper portion on which the fixed contacts of the switches and the rotary supports for the armature are located. The movable contact springs are embedded in the insulating armature plate. A recess in the armature plate is adapted to accommodate the two-pole permanent magnet. The document does not disclose whether the permanent magnet is magnetized in its embedded state in the armature plate. In any case, a drawback is the large spacing between the two-pole permanent magnet and the core of the electromagnet causing a large ferromagnetic-free path in the closed magnetic flux path, which results in a large magnetic resistance in any position of the armature.
In order to be capable to implement small polarized relays, very strong permanent magnets are necessary. Such strong permanent magnets are available and include fractions of rare earths. However, because of the strong attractive forces between the magnets, their handling from a supply of individual magnets is difficult, not only in terms of the adhesion of the magnets to each other, but also in terms of keeping the pole faces free of chips and dust particles during installation. In terms of production technology it is more favorable to use a piece of material of an unmagnetized ferromagnetic alloy and to “magnetize” the “precursor” once installed in the relay. However, magnetization in place using high field strength involves the risk that other components of the magnetic system of the relay might be damaged due to strong induced voltages and currents, in particular the coil of the electromagnet.